Quartz oscillator plate



16, 1948. Q pfio 2,437,914 7 QUARTZ OSCILLATOR PLATE I Filed Dec. 15,1944 INVENTOR CLIFFORD FRONDEL ATTORNEYS Patented Mar. 16, 19482,437,914 QUARTZ OSCILLATOR PLATE Clifiord Frondel, Flushing, N. Y.,

Reeves-Ely Laboratories, Inc., New York,

a'ssignor to N. Y.,

a corporation of New York Application December 15, 1944, Serial No.568,328

16 Claims.

This invention relates to quartz oscillator plates and has for itsobject certain improvements in the method of manufacturing oscillatorplates made of quartz or equivalent material.

In the manufacture of so-called BT quartz oscillator plates, forexample, automatic or semiautomatic machines are generally employed inthe initial and intermediate states. The final finishing of the platesis, however, still largely a hand operation, the work being done byhighly skilled operatives, usually called finishers. In finishing theplates, physical dimensions of the order of sub-millionths of an inchare involved. The finisher is usually provided with a frequencycheckingdevice, a flat glass plate, fine abrasive, an etching solution, water, abrush, cleaning solutions, lint-free towels, a micrometer, an opticalfiat, a small square, etc.

The finisher receives the plates, sometimes called blanks, as they comefrom mechanical lapping machines, the plates having been cut tosubstantially proper length and width and usually brought close to, butless than, the desired oscillating frequency. In a plate desired to havea final frequency of, say, 8,000 kc., the machine lapping or otherpre-hand-finishing treatment is stopped when the plate is from roughly afew hundred cycles up to ten or more kilocycles under the final desiredfrequency. A preliminary frequency check is then made by comparing thefrequency of the plate with that of a standard plate having a knownfrequency. This gives the finisher a general idea how much hand lappingthe plate should be given. To reduce the plate to its proper thickness,and hence to increase its frequency, the finisher grinds the plate in amixture of the abrasive and water on the flat glass plate, keeping thefaces of the plate as fiat and parallel as possible. The plate is nextthoroughly cleaned and dried, after which its frequency is again tested.This is done by inserting the carefully cleaned plate in a holder,plugging the holder into an oscillator circuit and noting whether or notthe plate has reached the desired oscillating frequency. The lapping ofthe major plane surlater-plate industry. Thus, in the so-called aciddipor etching process, the plates as obtained at the completion of themachine lapping are brought up to the desired frequency by dipping themfor the required length of time into a solvent for quartz. This solvent,which may be, for example, hydrofluoric acid, removes quartz from thesurface of the plate and thus acts to reduce the thickness of the plateto the desired value. This process, as with hand lapping, requires anintermittent, successive, series of treatments and measurements,especially in the final stages, to ensure that the desired frequency isexactly attained. The rate of etching of different plates of the sameinitial frequency is not identical, due to variations in the cleanlinessof the surface, the roughness of the surface, and other factors, so thata uniform, timed, procedure for all plates can not be set out. In stillanother method of finishing plates to the desired frequency, the platesare tumbled with an amount of coarse abrasive in a container until thefrequency apfaces of the plates usually is accompanied by a Y lapping orbeveling of the edges of the plates; this operation, by removingroughness and other imperfections from the edges and by altering theedge dimensions, gives the desired degree of activity. so-called, to theplate.

The finishing of a plate to its desired frequency also may beaccomplished in other ways, and a number of techniques other than handlapping have been and are being developed in the oscilproaches thatdesired. The plates are then removed, cleaned, and are adjusted to thedesired frequency either by etching or hand lapping.

Alternate hand lapping, cleaning and testing are required until theplate reaches the desired frequency. The activity of the plate isdetermined by its dimensions, contour, parallelism, absence of flaws,cleanness, etc. These physical characteristics are checked, changed, andrechecked until the desired activity is obtained. The frequency of theplate changes with changes made to the plate to obtain the desiredactivity, so that the finisher must coordinate the numerous variablesgoing into the finishing operation to obtain a combination of conditionsthat yields a plate of predetermined activity and frequency.

Hand finishing by these methods of the oscillator plates is a tedious,slow, delicate and costly operation at best and leaves much to bedesired. The human factor is an exceedingly important element in thesefinishing operations and the results obtained tend naturally to varyfrom person to person,

technique employed at the timejby each finisher.

depending upon the particular As a result of my investigation I havediscovered that the frequency and certain other characteristics ofpiezo-electric bodies may be adjusted or varied without altering thephysical dimensions of the body, such as by grinding, etching r platingwith a metal or other material. The frequency of oscillation of quartzoscillator plates, for example, may be varied continuously and thisvariation may bebrought under continuous visual control as by anappropriate meter. This permits the frequency to be adjusted exactly toa predetermined value or range merely by following the frequencyvariation on a meter and stopping the treatment at the desired value orwithin the desired range. This is not possible in present methods ofmanufacture of piezo-electric bodies which, as noted above. involve adiscontinuous alternatlng process of grinding or etching. cleaning andtesting. The frequency of oscillation of quartz oscillator plates may,for example, be readily adiusted to a desired value with an accuracy upto 1 cycle or greater, dependingprimarilyontheaccuracyofthemcasuringdevice employed. 'rhis accuracycannot be accomplished by the conventional method of grinding or etchingbecause the amount of grinding or etching on which the change offrequency and accuracy depends cannot be accurately controlled ormeassured. and the change in frequency itself cannot be observedcontinuously. I

The frequency of a piezo-electric body that has been put into arelatively stable state by means of baking, etching with a solvent forquartz, or other treatment. such as for the purpose of eliminating orreducing spontaneous variation with time in the frequency or activity ofthe piezoelectric body, can be adjusted without destroying the stabilityof the piezoelectric body. This is not possible by present methods ofmanufacture. For example, if a number of quartz oscillator 4 comprisesthe step of treating quarts oscillator plates to the action of cathoderays (electrons) adapted to decrease their frequency of oscillatim.

plates are brought by grinding or etching to a desired frequency, andare then baked or otherwise treated. for the P pose of stabilization, itis foimd that the frequency often changes erratically from the originalvalue and must then be adjusted by additional grinding or etching. Thisaction then destroys the stability of the oscillator plate and thepurpose of the original stabilizing operation is lost. This readjustmentcan now be accomplished without grinding or etching and without loss ofstability.

The frequency of oscillator plates may be adiusted, for example, withoutwetting them with water or other liquids and in an entirely drycondition. Water is commonly used in the conventional method offinishing to frequency by lapping with an abrasive or by etching, andhas been considered to contribute substantially to undesirable ageingand other phenomena in the finished oscillator plate. This dimculty maynow be obviated.

The frequency of a piezo-electric body can be adJusted while it iscontained in its permanent holder, whether this is of the contact(pressure), air gap, wire suspension or other type of mount. If desired,the frequency of the piece-electric body may be adiusted before it ismounted in its permanent holder.

The change in frequenc brought about by application of the invention isdownwards from the initial value, but the downwards change may bereversed. and the frequency restored to its original value, by suitabletreatment. The new technique is advantageous in the recovery ofoscillator plates that have been overshot by the methods of handfinishing. Oscillator plates that have increased in frequency over theupper tolerance due to ageing, or aged low activity lates that have goneover the tolerance after cleaning to bring up the activity, may besimilarly readjusted to their original frequency.

In accordance with the invention, the method Cathode rays consist of astream of electrified particles which are n atively charged. Asdisclosed in my co-pending application Serial No. 568,323, filedDecember 15, 1944, in mem'actice of the invention quartz oscillatorplates were sealed an evacuated cathode-ray tube itself to bring theplates in'oontact with the cathoderays. This method is. however,ineonvmient and an electron-gun type of molmting is preferred In theelectron-gun the cathode plate in the evacuated tube is replaced, forexample. y I wirefllament which is heated to ce bypassinganelectriccurrentthroughit. Abeamof cathode rays is shot down thetube when the filament is joined tothe negative depends on the potentialdifference between the cathode and the anode in the evacuated tube orelectron-gun: and the desired effect may be obtained by controlledbombardment of the oscillator plates. To reduce the frequency of theoscillator plates, th y re placed in the path of the stream of cathoderays as they emerge from the window of the electron-gun. The oscillatorplatesmaybeplaoedinthecircuitofaf queucr meter, so that the change tahngplace may be visually observed and the treatment terminated when theoscillator plates have reached a predetermined frequency, or at leastfall within a pre determined frequency range.

The change is frequency produced in oscillator plates by the cathoderays (electrons) is downwards from the original value. The change isprogressive and continuous during irradiation but finally reaches alimiting value, determined by factors within the quartz, beyond whichthere is no further change. The rate of change appears to dependprimarily on the intensity of the radiation, but in part on variationsin the Properties of the quartz from specimen to specimen and onpre-treatment of the quartz. The continuity of the change is of greatimportance from a manufacturing point of view. The downward direction ofthe change is also of particular advantage.

The downward change in i brought about by the cathode rays is permanentunder ordinary conditions, but can be revemed and the oscillator platebrought back to its original frequency by baking at a suitably elevatedtemperature or by irradiating the plate with ultra-violet rays.Ultra-violet rays reverse the action of the other type of radiation. Theability to reverse the downward change is a great advantage, In otherwords, the oscillator plates may be adjusted downwards and upwards infrequency r peatedly by the proper treatment.

The rate at which the downward change in frequency of the oscillatorplates can be effected and the total amount of change is influenced bythe temperature at which the quartz is held during irradiation, and bypreviously baking the quartz at a suitably elevated temperature.

These and other features of the invenflon will be better understood byreferring to the accompanying drawing, taken in coniimction with thefollowing description, in which:

Fig. 1 is a ditic representation of a cathode ray (electron) gun showinga quartz oscillator plate positioned before a window for anode terminall3 and a plurality of anodic defining shields I4, I42. The other end ofthe tube is provided with a window l5 through which the cathode rays(electrons) l6 may freely pass. A quartz oscillator plate I! is shown infront of the window, the plate being held on a sliding holder l8 movablein an upper track l9 and a lower track 20 by means of a handle 2 l.

Referring next to Fig. 2, the apparatus shown comprises a similarevacuated cathode ray (electron) gun l with a quartz oscillator plate I!located in front of the window i of the tube. in this case, however, theoscillator plate is mounted in a holder 25 of conventional construction.The casing of, and the electrode within, the holder around theoscillator plate are shown broken away, for convenience. The holder is,in turn, connected with a frequency meter 26 by means of a pair of leads21 and 28. The frequency meter may be of conventional design, having aneedle 29 adapted to move back and forth over a graduated frequencyscale 30, preferably divided to indicate cycles per second.

When cathode filament I2 is joined to a negative terminal and anodeterminal i3 is joined to a positive terminal of a source of directcurrent (not shown), and such direct current is passed through thefilament, it is heated and results in the thermionic emission of thestream of cathode rays (electrons) IS. The cathode rays (electrons) i6are made to form a beam of desired cross section by means of deflectingshields H,

M, which also direct the cathode rays to and through window i5 ontoquartz oscillator plate ii. The effect of the cathode rays (electrons)on the oscillator plate is gradually to decrease its frequency ofoscillation. The bombardment of the oscillator plate with the beam ofcathode rays may be conducted until the oscillating characteristics ofthe oscillator plate fall within a predetermined range or reach apredetermined value.

When using apparatus such as that disclosed in Fig. 2, the predeterminedfrequency range or value may be noted visually on frequency meter 26.When needle 29 is deflected until it points at the desired frequency orfrequency range indicated by scale 30, the oscillator plate is taken outof the beam of cathode rays or the beam of cathode rays is shut off.

The rate of change of frequency during irradiation is rapid, at first,but drops off with time and distance, finally to approach a limitingvalue. The magnitude of the limiting value varies with differentspecimens of quartz. This variation, which in the extreme cases so farencountered is about tenfold, appears to depend primarily on apredisposing feature in the quartz itself. The actual rate of change infrequency in a given oscillator plate varies with the conditions oftreatment, and primarily with the intensity of radiation. The decreasein frequency during irradiation is accomplished with little, if any.significant change in activity.

As previously noted, the frequency of quartz oscillator plates alsoundergoes a change when the plates are treated with ultra-violet rays;the change in frequency, however, being upwardly tions.

instead of downwardly. Oscillator plates irradiated as described abovein order to decrease their frequency may be reverted in frequency totheir initial value when exposed, for example, to a powerfulquartz-mercury lamp. The'change is accelerated by heating the quartzoscillator plates to 150 C. during irradiation with the ultra-violetrays.

The use of ultra-violet rays offers an impor tant advantage. If for somereason the frequency of an oscillator plate should be decreased too muchby the other type of radiation disclosed.

.its frequency may be increased to the desired value. The use ofultra-violet light rays is more particularly described and claimed in mycopending application Serial No. 568,330, filed December 15, 1944.

It will be clear to those skilled in this art that the invention lendsitself to numerous modifica- The oscillator plates may be irradiatedwhether plated or unplated, coated or uncoated. In accordance with theinvention the oscillator plates may, for example, be plated with a metalsuch as gold, silver, aluminum or an alloy which may serve the purposeof making a better or more intimate electrical contact with or act aselectrodes; or which may serve as a protective or stabilizing films. Theplates may, for example, be coated with amorphous silica or organicplastic or other material which may serve the purpose of protective orstabilizing films. In the case of oscillator plates that have beenprotected or stabilized by a plating, coating or other treatmerit,including heating and ageing, the radiations herein contemplated areadapted nevertheless to modify the oscillator plates so as to vary theiroscillating characteristics; and irradiation of the plates may beconducted until their frequency of oscillation reaches the desired valuewithout substantial loss of stability. The plates may be adjustedupwards or downwards in frequencyrepeatedly by use of the properradiations.

It also is possible to adjust the plate to have a desired frequency at agiven temperature by irradiating the plate, and bringing it tofrequency, while it is held at that temperature in a suitable heating orcooling contrivance. This is not easily accomplished by the conventionallapping or etching techniques of finishing plates.

The rate of change of frequency of the plate during irradiation and alsothe total amount of frequency change that can be obtained (saturationvalue) can be modified by baking the quartz plate at a suitabletemperature before it is irradiated. Thus, baking the quartz plate at asuitably elevated temperature has been found to increase both the rateof change and the amount of change of frequency over that which wouldobtain if the plate had not been baked beforehand. The increase in ratebrought about by baking between 250 and 350 C. ranges up to two-fold.and there is an accompanying increase so that the change in frequency ofoscillation which takes place may be visually observed and theirradiation stopped when the plates have attained the desired frequency.The type of permanmt holder, for example, may be of-the pressure orclamp, air-gap, combined pressure and air-gap, wire-support,mechanically or hermetically sealed, temperature-controlled ortemperature protected, or the multiple-type. If the oscil lator platesare mounted in a Permanent holder, the radiations go right through theplastic, glass or metal shell or housing of the holder. A sufficientlypenetrating radiation must, of course, be eml w This practiceisespecially useful in the case of oscillator plates supported betweenwire mounts in thin-walled vacuum holders. If the oscillator plates arenot .mounted in a holder, they may be held, for example, in paper oraluminum foil envelopes which protect them from moisture, dust andgrease spots from handling.

It also is convenient under certain circumstance; to irradiate a largenumber of plates simultaneously. This can be done, for example, ystacking the plates together and placing the stack directly in front ofthe window, face on. line amount of frequency change thus brought aboutis not uniform through the stack, but is greatest in the first plate,considerably less in the second, and then decreases more slowly insucceeding plates.

While the practice of the invention has been described with respect tomemo-electric material in the form of quartz, it will also be clear tothose skilled in this art that the invention is applicable to thetreatment of other piezo-electric materials, such as Rochelle salts,tourmaline, tartrates, etc. The invention is applicable to the treatmentof any useful pieao-electrl material the frequency and oscillatingcharacteristics of which are to be varied under controlled conditions.

I claim:

'1. In the manufacture of quartz oscillator plates,]the hnprovementwhich comprises treating each oscillator plate with cathode rays adaptedto decrmse its frequency of oscillation.

2. In the manufacture of quartz oscillator plates, the improvement whichcomprises treating each oscillator plate with cathode rays adapted todecrease itsfrequency of oscillation, and terminating the treatment ofeach plate with said cathode rays when its frequency of oscillationreaches a undetermined value.

3. In the manufacture of quartz oscillator plates, the improvement whichcomprises treat-- ing each wclllator plate while mounted in a holderconnected to a frequency meter to the action of cathode rays adapted todecrease the frequemy of oscillation of the plate, and terminating thetreatment of each plate with said cathode rays when its frequency ofoscillation reaches a predetermined value.

4. In the manufacture of quartz oscillator plats, the improvement whichcomprises treating each plate while mounted in a holder connected to afrequency meter to the action of cathode rays adapted to pass throughthe housing of the holder and to decrease the frequency of oscillationof the plate, and terminating the treatment of each plate with saidcathode rays when its frequency of oscillation reaches aprevalue.

5. In the manufacture of quartz oscillator plates, the improvement whichcomprises treating each plate while at a predetermined temperature 8with cathode rays adapted to decrease its frequency of oscillation, andterminating the treatment of the plate with said cathode rays when itsfrequency of oscillation reaches a predetermined value.

6. In the manufacture of quartz oscillator plates, the improvement whichcomprises maintaining each oscillator plate at a predeterminedtemperature while mounted in a holder connected to a frequency meter,treating the plate while at said temperauire with cathode rays adaptedto decrease the frequency of oscillation of the plate, and terminatingthe treatment of the plate with said cathode rays when its frequency ofoscillation reaches a predetermined value.

7. In the manufacture of quartz oscillator plates, the improvement whichcomprises maintalning each oscillator plate at a predeterminedtemperature while mounted in a holder connected to a meter, treating theplate to the action of cathode rays adapted to pass through the housingof the holder and to decrease the frequency of oscillation of the plate,and terminating the treatment of the plate with said cathode rays whenits frequency of oscillation reaches a predetermined value.

8. In the manufacture of quartz oscillator plates, the improvement whichcomprises grinding each oscillator plate to a thickness beyond thatrequired to increase its frequency to a predetermined value, andtreating the ground plate with cathode rays adapted to decrease itsfrequency of oscillation.

9. In the manufacture of quartz oscillator plates, the improvement whichcomprises grinding each oscillator plate to a thickness beyond thatrequired to increase its frequency to -a predetermined value, treatingthe ground plate with cathode rays adapted to decrease its frequency ofoscillation, and terminating the treatment of each ground plate withsaid cathode rays when its fre quency of oscillation reaches apredetermined value.

10. In the manufacture of quartz oscillator plates, the improvementwhich comprises etching each oscillator plate to a thickness beyond thatrequired to increase its frequency to a predetermined value, treatingthe etched plate with cathode rays adapted to decrease its frequency ofoscillation, and terminating the treatment of the etched plate with saidcathode rays when its frequency of oscillation reaches a predeterminedvalue.

11. In the manufacture of quartz oscillator plates that have beenstabilized by baking, acid washing or other treatment and that have afrequency of oscillation hisher than desired, the improvement whichcomprises treating each stabilized oscillator plate with cathode raysadapted to decrease its frequency of oscillation, and .terminating thetreatment of each stabilized plate with said cathode rays when itsfrequency of oscillation reaches a predetermined value.

12-. In the manufacture of quartz oscillator plates, the improvementwhich comprises treating each plate to the action of cathode raysadapted to decrease its frequency of oscillation, treating the plate tothe action of ultra-violet light rays adapted to increase its frequencyof oscillation. and terminating the treatment of the plate with theultra-violet rays when its frequency of oscillation reaches apredetermined value.

13. In the manufacture of quartz oscillator plates, the improvementwhich comprises heating each plate to an elevated temperature tosensitize it to frequency change, treating each sensitized plate tocathode rays adapted to decrease its frequency of oscillation, andterminating the treatment of each plate with said cathode rays when itsfrequency of oscillation reaches a predetermined value.

14. In the manufacture of quartz oscillator plates, the improvementwhich comprises heating each plate to an elevated temperature tosensitize it to frequency change, treating each sensitized plate to theaction of cathode rays adapted to decrease its frequency of oscillation,treating the plate to the action of ultra-violet light rays adapted toincrease its frequency of oscillation, and terminating the treatment ofthe plate with said ultra-violet light rays when its frequency ofoscillation reaches a predetermined value.

15. In the manufacture of quartz oscillator plates, the improvementwhich comprises heating each plate to an elevated temperature tosensitize it to frequency change, treating each sensitized plate to theaction of cathode rays adapted to decrease its frequency of oscillation,heating the plate so treated to increase its frequency of oscillation,and terminating the heating of the plate when its frequency ofoscillation reaches a pre determined value.

16. In the manufacture of oscillator plates the step comprising reducingthe frequency of the oscillator plate by treating the same with cathoderays.

CLIFFORD FRONDEL.

